Official Luthiers Forum!

All thats very interesting, thanks guys.
I wonder how much pressure go-bars put on?

_________________
Jim Watts
http://jameswattsguitars.com

[QUOTE=Jim_W] All thats very interesting, thanks guys.
I wonder how much pressure go-bars put on?[/QUOTE]

You can easily measure this with a bathroom scale between the go deck and the go bar. Mine, which are 1/4" fiberglass and about 30" long put out about 9-15 lb of force if I remember correctly.

You also may find it interesting that as you compress the bar, the force goes up somewhat linearly, until you get to the buckling point, and then it stays rather steady even if you increase the amount of bow in the go-bar. I believe this behavior is described by Euler's buckling equations.

Sounds to me like go-bar and vacuum clampers need to follow the part about getting a perfect fit and spreading the glue evenly. There is no way you could clamp a 5/8" x-brace with go-bars without a great fit. Each x-brace is about 10 square inches of gluing area requiring 1000 lbs of force. That is around fifty go-bars and impossible with vacuum clamping.

No wonder we have brace failers...

_________________
Joe Beaver
Maker of Sawdust

[QUOTE=Joe Beaver] Sounds to me like go-bar and vacuum clampers need to follow the part about getting a perfect fit and spreading the glue evenly. There is no way you could clamp a 5/8" x-brace with go-bars without a great fit. Each x-brace is about 10 square inches of gluing area requiring 1000 lbs of force. That is around fifty go-bars and impossible with vacuum clamping.

No wonder we have brace failers... [/QUOTE]

You're right - the very low clamping pressure could explain why people sometimes have problems with braces coming loose.

Another reason could be that people often prepare the braces curved side by sanding it in a radius bowl.

A sanded surface (especially with a coarse grit like #60 that some use) makes for a poor glue joint. The rough, sanded surface, combined with low clamping pressure might be resulting in an effectively thick glue line - even if enough glue is used. None of the glues usually used for bracing are good gap fillers.

Spruce-on-spruce glue joints should NEVER fail - it is one of the easiest, most reliable woods to glue.

Phil

Phil,

After considering the info here I've decided against getting a radius dish and go-bar setup. Maybe when I am confident in my ability to get that elusive 'perfect fit' I will reconsider. I'll stay with radiusing my braces on a belt sander and clamping with lots of cam clamps. I get about 65 lbs with those. I'll add sanding the parts to 320 grit. That should help.

_________________
Joe Beaver
Maker of Sawdust

I use a plane setup to radius braces: just a shim on the sole of the plane behind the cutter. Depending on the thickness of the shim and the distance from the cutter you can make any radius you need. It took me a few trials to get it just right, but then I scribed lines on the sole of the plane so that I could reproduce it. Stick the shim on with CA. A freshly planed surface is the best for gluing.

Ditto on Toddstock comments

Joe, I would hate to think about not having my Go-Bar Deck and radius dish. I understand the technical data being presented, however, if you create a good fit, well sanded surface, proper glue application, they work great.

Mike
White Oak, Texas

Mike,

I know a lot of people use go-bar decks with great success. I may try it one of these days. It sounds to me that if you use care with surface prep, fit and even glue spread as you, Todd, Alan and other experienced builders do, go-bars should work fine. The process may be a little beyond my skill level right now and I don't mind doing it with just cam-clamps.

_________________
Joe Beaver
Maker of Sawdust

The other guys are "experienced builders", I am not in that category, a rookie by all standards. I use cam-clamps as well on my work board, I don't use any molds at this time. If that works for you, then I would stick with it. I used the cam-clamps before getting a Go-Bar set up on my first and it worked very well, guitar was less than stellar, but still fun. I jumped on the Go-Bar set up and radius dish after reading some threads here on the OLF.

Happy building!

Mike
White Oak, Texas